1. Field of the Invention
The present invention relates to a control apparatus for an internal combustion engine including first fuel injection means (in-cylinder injector) for injecting fuel into a cylinder and second fuel injection means (intake manifold injector) for injecting fuel towards an intake manifold or intake port. Particularly, the present invention relates to an apparatus for controlling the internal combustion engine such that a knock sensor in a KCS (Knock Control System) does not erroneously sense vibration other than knocking.
2. Description of the Background Art
An internal combustion engine is well-known, including a first fuel injection valve (intake manifold injector in the background art) for injecting fuel in the intake manifold of the engine and a second fuel injector valve (in-cylinder injector in the background art) for constantly injecting fuel into the engine combustion chamber, wherein fuel injection from the first fuel injection valve is inhibited when the engine load is lower than a predetermined load setting, and fuel is injected from the first fuel injection valve when the engine load is higher than the predetermined load setting. The overall injection quantity that is the total of the fuel injected from the two fuel injection valves in this internal combustion engine is determined in advance as the function of the engine load. The overall injection quantity is increased as the engine load becomes higher.
The second fuel injection valve (in-cylinder injector) is mounted so as to directly open towards the combustion chamber of the internal combustion engine, and directly injects the fuel pressurized by the fuel pump into the cylinder. The second fuel injection valve must set the fuel pressure 20–50 times higher than that of the first fuel injection valve. The second fuel injection valve employs a robust spring to achieve such a high oil pressure and a high voltage circuit that can achieve an intensive electromagnetic force for high response. The second fuel injection valve is mounted so as to directly protrude into the combustion chamber, and is used under the environmental condition of high pressure, high heat, and intensive vibration by the combustion. Therefore, the second fuel injection valve is apt to exhibit function degradation and occurrence of an abnormal event due to carbon clogging and the like, as compared to the fuel injection valve conventionally and widely employed in manifold injection type internal combustion engines. Degradation in the performance and occurrence of an abnormal event at the fuel injection valve will prohibit proper operation of the internal combustion engine, resulting in the possibility of posing problems such as power degradation and increase in the emission of harmful gas components.
Japanese Patent Laying-Open No. 10-318027 discloses a fuel injection valve abnormality detecting device for an internal combustion engine including such an in-cylinder injector. This fuel injection valve abnormality detecting device includes, in the fuel injection internal combustion engine, signal detection means (knock sensor) for detecting a signal reflecting the vibrating state of the internal combustion engine, and means for determining abnormality at the fuel injection valve by obtaining a signal related to the opening/closure of the fuel injection valve through the signal detection means.
In accordance with this fuel injection valve abnormality detecting device for an internal combustion engine, an abnormal event at the in-cylinder injector can be detected through the vibrating state of the internal combustion engine detected by a knock sensor. In other words, vibration in connection with an operation of the in-cylinder injector can be sensed by a knock sensor, and an abnormal event at the in-cylinder injector can be detected based on the sensed result.
Japanese Patent Laying-Open No. 11-229951 discloses a knocking control device that can properly conduct knocking determination using a knocking sensor, impervious to variable valve timing (VVT) control, in a multiple-cylinder internal combustion engine with a VVT control device. This knocking control device is provided at a multiple-cylinder internal combustion engine with a variable valve timing control device for controlling the opening/closing timing of at least one of the intake valve and exhaust valve of each cylinder in the internal combustion engine according to the internal combustion engine operation state. A detection signal from the knock sensor that detects the mechanical vibration of the internal combustion engine is fetched during a predetermined knock determination period in the detonation stroke of each cylinder in the internal combustion engine. Determination is made whether knocking has occurred or not in the internal combustion engine based on the fetched detection signal. Knocking control is effected by adjusting the ignition timing of the internal combustion engine based on the determination result. The knocking control device includes knock determination period setting means for setting a knock determination period such that the closing timing of the intake valve or exhaust valve does not overlap with the knock determination period, based on the opening/closing timing of the intake valve or exhaust valve under control of the variable valve timing control device.
According to this knocking control device of an internal combustion engine with a VVT control device, a knock signal is fetched from a knock sensor, and the knock determination period to carry out knocking determination is set so as to avoid overlapping with at least the valve closing timing, based on the timing of the intake valve or exhaust valve under control of VVT. A knock signal including the seating noise of the intake/exhaust valve is fetched during the knock determination period to prevent erroneous determination of knocking for accurate execution of knocking control.
Japanese Patent Laying-Open No. 10-318027 teaches that vibration in connection with an operation of the in-cylinder injector is sensed by a knock sensor. Japanese Patent Laying-Open No. 11-229951 teaches that control is effected such that the knock determination period does not overlap with the closing timing of the intake valve and exhaust valve. Thus, it is difficult to sense knocking at high accuracy by a knock sensor when vibration in connection with the operation of the in-cylinder injector overlaps with the knock determination period in an engine with an in-cylinder injector.
Although control can be effected such that the closing timing of the intake valve and/or exhaust valve does not overlap with the knock determination period through the VVT based on the teachings of the patent documents set forth above, control cannot be effected such that the vibration in connection with an operation of the in-cylinder injector does not overlap with the knock determination period. If the injection period of the in-cylinder injector is shortened, the required fuel injection quantity may not be satisfied. There is a possibility of having difficulty in ensuring the engine performance.